The present invention relates broadly to constant false alarm rate radar detector apparatus, and in particular to a target discrimination apparatus for a constant false alarm rate radar detector.
For the conventional adaptive CFAR detector circuitry, the signal in the detection window is compared to the threshold value which is the product of the base multiplier and the clutter average in the CFAR block. A report or target candidate is declared if the result of comparison is positive. There is a problem for the conventional adaptive detector which fails to accommodate the target-to-target interference as targets pass through the clutter cells in the detector. The clutter cells are usually referred to as a CFAR block which forms the clutter average. When the target enters the CFAR block, the target signal will raise the clutter average and degrade the ability to detect the nearby target incidently located in the detection cell. The detection degradation due to the target interference has been found to be unacceptable especially if radar operates in very heavy target environments. A target with signal to noise ratio of 20 dB will yield 1.5 dB detection degradation if target occupies only 2 percent of CFAR block. The degradation is found to be even more severe if target range extent or amplitude is large. Multiple targets such as a fleet of naval vessels or aircraft are not unusual in the real radar environment. Previous attempts to alleviate the target interference include the technique of increasing the CFAR block size. However, the technique can only alleviate but not totally eliminate the interference effect. Furthermore, there are some cases (for example high pulse repetition frequency) where the CFAR block cannot be extended. Introducing a target discrimination apparatus into the automatic adaptive one-sided CFAR circuitry will solve the problem. The uniqueness of this apparatus will prevent the candidate target from moving into the CFAR block. Thus, the clutter average calculated from the CFAR block will not be contaminated by the target and no detection loss will result from the presence of multiple targets.